Severe droughts devastate eucalyptus trees that pre-date Ice Age
University of South Australia Media Release
South Australian scientists have documented the catastrophic decline of a stand of red stringybark in the Clare Valley, a tree species that has survived in the region for 40,000 years but is now at risk of extinction due to climate change.
Two severe droughts driven by climate change since 2000 are blamed for “staggering losses” of an isolated population of the South Australian species Eucalyptus macrorhyncha in the Spring Gully Conservation Park.
Multiple surveys led by University of South Australia environmental biologists Associate Professor Gunnar Keppel and Udo Sarnow have recorded tree and biomass losses of more than 40 per cent, during the Millennium Drought from 2000-2009 and the Big Dry from 2017-2019.
More than 400 trees were monitored over 15 years, within two years of their dieback first being reported in 2007.
The scientists say that approximately 250 tonnes of biomass per hectare have disappeared.
“In areas that experienced complete dieback, drooping she-oaks remain as the only trees, suggesting that the red stringybark ecosystem could be replaced by a more open woodland,” Assoc Prof Keppel says.
The research team, which included scientists from the State Herbarium of South Australia and University of Adelaide, has published their findings in the journal Science of the Total Environment.
Genetic data show that the red stringybark trees in the Clare Valley have been isolated from their closest relatives in the Grampians National Park in Victoria for about 40,000 years. This predates the Ice Age when Australia was much drier and cooler.
“The Clare Valley provided a safe haven that facilitated the survival of the red stringybark during this arid period. However, current climate change is different from the last glacial age. It is associated with much hotter temperatures compared to the preceding time periods, which were cooler but much drier.”
The team used trees marked by the Department of Environment and Water to document the progress of the eucalyptus dieback in the Clare Valley.
During the Millennium Drought, sites with less water and on flatter ground were most severely affected, while sites subjected to the greatest heat stress were most susceptible during the Big Dry.
Dieback is further compounded by intensive agriculture and viticulture in the Clare Valley, potentially adding more stress and preventing migration to sites that may facilitate the species’ survival.
But there is hope, researchers say.
“Mortality was much lower on the south and east-facing slopes – sites that received less sun and therefore less heat and drought-stress,” Sarnow says.
“In these locations, some regeneration was also evident. Hopefully, the population can persist in pockets that provide milder microclimates.
“If we can manage the population in Spring Gully Conservation Park, protecting these microclimates, we may be able to save this unique element of Australian biodiversity.”
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An excellent example of microclimate effect where south facing slopes get less solar radiation due to aspect and eastern slopes get ”cooler” morning radiation, both compared to level sites at the ”same” location. This effect would be well known to vineyards.
This sort of thing is happening all over the country. River red gums along the Murray-Darling and other large river systems, snowgums in the Australian Alps, Miena cider gums on the Central Plateau and Nothofagus in the western rainforests hare in Tassie. I’ve read about the Karri forests in the west having major problems, too. But, of course, it’s only the environment that keeps us alive so it doesn’t matter to those who call the shots (the fossil fuellists).
It’s also occurred to me on many occasions when I’ve been on the road and observing Eucalyptus dieback across many regions, that the wholesale clearing of the land has had a devastating impact on the remnant flora and most likely due to the destruction of the ubiquitous fungal communities that existed prior to the introduction of European farming practices, viz. the use of machinery that rips up the soils; ploughs, tynes, discs and whatever else agricultural engineers dreamt up to enable the shattering of soil profiles, the transformation of clods into crumbs and thence into dust and hence to be blown or washed away – massive erosion being a corollary of intensive farming practice in this country – along with the concomitant loss of biota and the intrinsic & essential relationships between macroflora and their fungal symbionts.
No wonder the countryside is ill! No wonder the indigenous people are sickened at heart. No wonder it is impossible to farm without massive inputs of chemicals – fertilisers and the ‘cides’ – fungi, herbi, and pesti.
I was born and through to my late teens grew up alongside the Yarra in Melbournes urban fringe. I know that environment, its secondary growth post wood-harvesting years, and even more so its riparian environment. In my younger years I witnessed the bush slowly repairing itself after the earlier ravages and infestations from colonisation.
Years later I returned to the locale, and lived there for 20 years, working in concert with the Landcare community to eliminate the environmental weeds and revitalise and replant and nurture the endemics. Toward the end of and following the millennium drought, the big old native trees started dropping like flies, and this trend appears to now be accelerating due to the ravages of air pollution and climate change.
Sadly I watched as the renegades that are the State Parks authorities blunder through eliminating the natural vegetation (deemed a fire risk) that were critical precursor plants to reforestation, and which also provided necessities for the biota essential for maintaining the chain of native fauna.
There appeared to be a misunderstanding verging on hatred of the Oz bush and some lunatic notion of paradise represented by European fairytales lodged in their tiny minds.
In Vic, the govt continues to hack down the remaining old-growth forests. Go figure, politics is an ass seeking ignorance.